Gordon Gibby <ggibby@...>
Well, I'm several days BEHIND on what I had planned on this project, but I have some baseline results finally. (Had pancreatitis last week and gallbladder removed Monday and laid up a bit, then struggled several days with an open-repeater ics-ctrl repeater controller raspberry pi project to completion).
First goal was to develop a homebrew measurement lab in place of a spectrum analyzer, to allow baseline measurements of harmonic output from a stock ubitx v3/4. (Prior to modification to add in a daughterboard filter relay repair described previously.)
Using a 50 ohm/16.6K ohm voltage divider built on top of a Heathkit cantenna ( 2 100 ohm in parallel to make the 50 ohm, checked with very low SWR well beyond 30 MHz on antenna analyzer to be sure not wirewound resistors) and 6 100K resistors in parallel to make the top of the voltage divider), created approximatelly 50 dB attentuator.
Then double shielded BNC coax patch cord to selected bnc attenuator right at the input to an ICOM 718 receiver.
Tonight was initial tests. First problem: V4.3 of software would not go into CW mode no matter what I tried on the key terminals. Finally gave up and reverted to my own modified v2.0 of the ubitx code which does transmit. Next problem was my radio shack "wattmeter" indicates rather low outputs.....but may not be accurate at all so I just went forward.
"Attentuator" is the ADDITIONAL attenuator beyond the estimated 50 db at the cantenna.
Mode Freq Meas.Watts Attenuator Fundamental 2nd Harmonic 3rd Harmonic 4th Harmonic 5th Harmonic
CW 3.505 2 20 dB S9+25 S8 S8 not meas S8
CW 7.080 1 20 dB S9+25 S6 S8.5 not meas not meas
All I have is the little LCD screen of the ICOM 718....but the readings were quite steady and the tuning in of the signal was not critical at all. For the very first crack at this EVER in my life, I was much more impressed with the measurement setup than I was with the problems I was inhaving the little uBitx to perform for me to allow testing. I'll fiddle with this a bit more to be sure I'm happy with some baseline readings before I begin hacking traces and building the circuit board I have for the outboard relays. I may have some other "power meters" [these allare just simple rf voltmeters posing as wattmeters] and see if I get any more believable answers.
gordon gibby kx4z